Chemical analysis and the identification of biological materials has long been the domain of analytical biology, chemistry and physics. The methods used often require cumbersome laboratory instrumentation in a centralized laboratory and long sampling and analysis times. However, over the last few decades, the increasing awareness and concern regarding factors that influence health, safety, appliance performance, and the environment has created a demand for user-friendly technologies capable of detecting, identifying, and monitoring chemical, biological, and environmental conditions in real-time. In response to these needs, a successful commercial market focused on exploiting, simplifying, improving, and cost-reducing sophisticated laboratory procedures and hardware has emerged. Home CO2 monitors, drinking water purity monitors, and smoke detectors are now very common. Many of these devices have become requirements in new homes and workplaces. In addition to the environmental sensor products, there is a rapidly growing market focused on personal health monitors and health screening appliances. For example, there are a number of systems on the market today that provide sampling and analysis of blood for glucose monitoring. Analogous to the computing revolution, the evolution from centralized sensing to distributed and embedded sensing is well underway. Given these trends, it is safe to predict that intelligent, portable, wireless, web-enabled, self-diagnostic appliances exploiting a broad range of chemical and biosensor technology will be in demand in the near future.
An important, competing technology is chemically sensitive field effect transistors (ChemFETs). ChemFETs rely on chemically initiated electric field fluctuations above the two dimensional FET channel to modify the source-drain conductance. While ChemFETs exploit the same physical principles for detection as nanowires, they require large planar surface areas over the FET channel and lack the extreme sensitivity and discrimination enabled by the high surface-to-volume ratios of nanowires.
Other proposed detection schemes based on nanowires require that good electrical contacts be made to both ends on each nanowire that is used in a detector. Disadvantages of this approach include the requirement of placing and contacting individual nanowires which is expensive and time consuming, and that the yield of such devices with good electrical contacts may be low. Devices that are based on a single nanowire are also not very sensitive and can provide spurious signals.
In each of the applications above and with others, there is and will be an ever-increasing demand for lower detection limits, higher selectivity and sensitivity, portability and real-time response. Although substantial improvements in detector sensitivity and response have been achieved by leveraging advances in microelectronic, micromechanical, and microfluidic technologies, in order to meet the demands for real-time, single-molecule discrimination, continued and innovative improvements will be required. It is likely that these improvements will require the development of new technologies.